Poor repair of brake system after RV was delivered for service repair. Dealer found hose system failure on RH side of vehicle and failed to investige or replace opposite side. Root cause of issue not fulling investigated causing failure within 70 miles after repairs made at a cost of over $1400.00. This failure could have caused serious injury to person or persons. If root cause was properly determined dealer should have questions of opposite side of system could also fail during normal driving conditions. There is history data to the fact that problems with past units with same type of chassis has occurred in the past. Dealer stated only parts found defective were replaced but same part on opposite side of vehicle was not questions due to not finding failure during inpsection. NOTE: Failure would only occur during normal driving conditons. After discussion with service manager his statment was the dealership only replaces parts found defective when repairing units. Again this failure would only occur during driving. This condition will not occur when vehicle is setting in a parking lot or in storage.